1. Field of the Invention
This invention relates to a glass suitable for deposition by chemical vapor deposition ("CVD") techniques which has a softening (or "flow") point far below temperatures at which glasses currently used in the semiconductor industry flow.
2. Description of the Prior Art
The vapor deposition of phosphorus-doped silicon oxides onto a substrate is well-known. Such glasses are typically used to passivate the surfaces of integrated circuits made using silicon. Commonly denoted as "PVx" or "phosphorus doped vapox", glasses formed in this manner have very high reflow points in the range of 1000.degree. C. to 1100.degree. C. To reflow these glasses to remove sharp edges and provide curved, gradual-sloping surfaces on which conductive leads can easily be formed with gradual, rather than abrupt, changes in surface height, thereby to reduce the likelihood of such leads cracking or breaking, the integrated circuit must be heated to temperatures within the range of 1000.degree. to 1100.degree. C. Such high temperatures change the diffusion profiles of the various doped regions within the integrated circuit which give to the circuit its electrical characteristics. This is undesirable. Thus the fabrication of a semiconductor integrated circuit, particularly one using more than one level of conductive leads (known as a "multilevel" structure) becomes highly complicated with the final characteristics of the device differing somewhat from the characteristics of the device prior to the formation of the various levels of conductive leads.
The formation of glasses suitable for use as passivating and/or insulating layers in integrated circuits which reflow at temperatures significantly below the 1000.degree. C. to 1100.degree. C. temperatures at which glasses currently used in integrated circuits reflow is particularly important now that laser annealing and glass reflow techniques are becoming commonly used in semiconductor processing. In the past, various glass mixtures have been used or proposed to achieve lower reflow temperatures. Thus sedimented glasses have been proposed for use in the manufacture of integrated circuits with the constituents of the glasses being selected such that these glasses reflow at a substantially lower temperature than the reflow temperatures of commonly used phosphorus-doped vapor deposited oxides of silicon. Unfortunately, the techniques used to control the thicknesses of the deposited glasses and the technologies for depositing the glasses differ substantially from the techniques and technologies currently used in the semiconductor industry in the vapor deposition of oxides of silicon (both undoped and doped with phosphorus).